The best limescale inhibitor?


An admittedly rather biased look at the types of water ‘conditioners’ and limescale inhibitors available, from the smoke’n’mirrors stuff to what really works. Rule number one is DO NOT buy any limescale inhibitor where the ad/website says “water softener” when it clearly isn’t actually an ion-exchange water softener. That alone tells you everything about the company selling it...that porky pies are evident!


You may also be aware that many websites (when you do a search) show ‘Guarantee’ in their blurb. What is their guarantee - is it stated on their website? A particular limescale inhibitor was brought to our attention by a reader with their ‘10 year guarantee’...except they don’t tell you what that guarantee is!



Remember, when we say “in our experience”...

it really is in over 40 years of experience



So, what is hard water?

Rain droplets absorb carbon dioxide in the atmosphere and become a very weak acid...


When this water hits rock, like limestone, it becomes super saturated in metal ions like calcium and magnesium. This stays in the water in solution - ‘temporary hardness’ (that will come out again) and ‘permanent hardness’ (that won’t - it stays in the water). When water is heated, or even warmed, the limestone particles will precipitate out and form a solid again. This occurs at fairly low temperatures, but becomes a serious problem at anything over 63 degrees C.


This is a problem for ‘boilers’ and water heaters in areas of the country where limescale forms...



Hard water is a serious problem because it’s a great insulator of heat - it stops heat transferring, hence you have to heat the limescale in order to heat the water. A build-up of just a few millimetres will add a significant part to your energy bill.


It will also cause the failure of expensive water heating equipment in homes and commercial properties. So it’s a serious, costly problem. Many years ago, a man called Emmett Culligan was credited with inventing the first practical use of a water softener. Water softeners really do work, they take limescale out. However, their disadvantage is that they are bulky, expensive, use lots of water when backflushing (every week), and obviously use quite a lot of salt (which used to be cheap, but is no longer!).


Therefore, a different approach is needed. What if we don’t soften the water (because actually hard water is good for your health), but just stop the calcium from sticking?


We are plumbers. We have been doing ‘plumbing’ for over 40 years, and right in the middle of a hard water area, the Thames Valley. We’ve seen LOTS of limescale. We have chiselled it out of boilers at Reading Football Club back in 1976! We have vacuumed it out of industrial water heaters in hotels. We have dissolved tons of it in acid for three decades now.


However, we did spot that whenever we came across a plumbing installation that had no limescale, a ‘water conditioner’ was present that was using silicate-polyphosphate (Siliphos). It was obvious, right from the first two instances we witnessed that Siliphos was having a remarkable effect on limescale. So in 2003 we invented our own range of Siliphos-based limescale inhibitors.


Over the years, we have heard about every idea for stopping limescale, from magnets to fancy new ways. But we haven’t found that ANY OF THEM work. We’re not saying they don’t work (well, perhaps we are) but we are saying that we have absolutely no evidence of any of them working...none. Yes, we’ve read all the claims, but still no evidence.


‘Limescale inhibitors’ are split into two groups:


Chemical devices  -  non-chemical devices


The definitions sound obvious, but we’ll go there anyway. A chemical device uses a material to dose the water, or do something to the water, physically - it uses a ‘chemical’. Now don’t be put off from that word on health grounds, as sodium chloride and acetic acid is just salt’n’vinegar, remember! No one is going to sell you anything that is harmful in any way, as they would get prosecuted for doing so. Even we have to advise that a non-return valve is fitted whenever you install one of our devices - because the water companies insist on the water being the exact same ‘quality’ that they produce at their treatment plant as at your taps. So if you add any ‘chemical’ device to the water mains, you have to install a valve which stops anything in that device from allowing the water to back-feed back to the mains supply. Silicate-polyphosphate is a harmless, food-grade material, yet any device housing it still has to have a non-return valve fitted...even though silicate-polyphosphate is approved for drinking water both with the EU and the World Health Organisation!


Again, don’t think that adding chemicals is a bad thing, as the water companies have added enough of them, anyway!


So, there are also non-chemical devices. These use a way of affecting the water (or rather, are supposed to!) instead of a chemical. They could be magnets on the outside of the pipe, or zinc inside the pipe, or electronic waves, or even a combination of things.


LET’S BE CLEAR: If we found a non-chemical device (NCD) that worked to even reduce limescale, let alone stop it completely, then we would be selling it. Why wouldn’t we? But the fact is that we’ve been attending to hot water systems for over 40 years, and we’ve never found a single device (that isn’t chemical-based) that works. It’s THAT simple. If you think you have found such a device, then just read the box to the right at the top. Will the manufacturer of that device give you your money back in 10 years’ time if you found it wasn’t working?


The answer is NO. No manufacturer of a NCD will give you your money back.


Now, to us, that says everything. Why on earth would you buy it? Lots of claims are made, and manufacturers of such devices give you an impressive list of their customers, such as giant retail outlets, or even NASA. But when you contact these companies, they can’t verify the claims made. We heard of one limescale device company claiming that Coca Cola were one of their customers. So we phoned Coca Cola, and they didn’t know what we were talking about. The operator stated that the company is vast and employs almost 62,000 people, she didn’t have a clue where to start asking.


So what about chemical devices - will the makers of these give you your money back? Again, NO, they won’t - except us. Strangely (or perhaps not so strangely) companies producing phosphate limescale inhibitors won’t provide a performance guarantee like ours. The reason may be because of our picture to the right here, next to ‘Phosphate’ limescale inhibitors stop themselves from working (if they ever did) by blocking themselves just a few months after installation.


We’re not scientists, we’re plumbers. As we said, all we can give you is the benefit of our 40 years of experience of seeing hot water equipment right smack in the middle of a limescale hotspot of the UK. We have only ever found two things that really do work at stopping limescale: water softeners and silicate-polyphosphate (Siliphos) dosers.


Now, it is true that from time to time we hear of the claims of new devices, and we check them out, maybe even trial them. Still, after all these years, we haven’t found any that work. It would make our job of selling such things much easier if we did!


So, a look at the various methods of halting limescale - and if they work, or not!...



Most magnetic water conditioners simply have a mild magnetic field close to the water supply pipe. This is said (by manufacturers of these units) to induce a molecular change to the calcium salts. Such units are usually (but not always!) inexpensive, easy to fit, and require no electrical supply. Some types use a very cheap ceramic magnet. However, it is obviously clear that a weak magnetic field would NOT be effective. The magnetic field on passing water would have to be very strong.

In our experience, do they work?

NO...BUT we understand that some people have stated a difference, and some just want to comply with Part L of the Building Regulations. For that reason, we manufactured our own (with strong magnets) the LimeStop M.



An electrolytic ‘water conditioner’ is supposed to work by the use of dissimilar metals placed in the flow of water, being electrically connected. In the presence of water (an electrolyte) a ‘LeClanché’ (battery) cell is achieved. The metals develop an electro-magnetic force between them. This is meant to allow the addition of zinc metal ions in the water which, it is claimed, produces a permanent change to the calcium crystal morphology. Hard salts are encouraged to cling to each other rather than pipework, heating elements in appliances, etc. It does not require an electrical supply.

In our experience, do they work?




The electronic limescale inhibitor is meant to work by using a high frequency signal generator (0.5 - 100 kHz) which is applied through a direct connection to the pipe surface. The current induces a ‘field effect’ into the water which imparts energy at a molecular level to the water. As long as the water keeps this energy level, it is supposed to hold a greater amount of salts in suspension and encourage already existing salt deposits to re-dissolve. It requires an electrical supply. There is a company selling these to ignorant architects (there are a surprising number of ignorant architects!) for an enormous cost - and getting away with it!

In our experience, do they work?




Phosphate limescale inhibitors usually require a changeable cartridge with a dosing valve fitted. The idea is that water will flow partly through the unit and thus be dosed with phosphate particles. This is meant to suspend the calcium particles. Unfortunately, the dosing valve becomes clogged with phosphate very quickly after fitting - thus ceasing any effect the unit may have. We have yet to see a single one that hasn’t blocked itself! The picture, (above-right - yet another we’ve removed) tells the story for us. The pic shows that the dosing valve is completely blocked with phosphate. When you replace the cartridge, you don’t get to see this view! So you replace the cartridge thinking that it’s still working! It’s wasted money. No electrical supply required.

In our experience, do they work?



Aqua Conditioners

These use a bed of resin in a chamber about the same size and shape as a scuba-diving oxygen cylinder. It is called nucleation-assisted crystallisation. The idea is that the resin will hold onto the calcium as it passes. When the molecules get saturated with calcium, they get trapped in a post-filter. They are quite expensive for what is a piece of plastic.

In our experience, do they work?




‘Siliphos’ is a widely-trusted food-grade material proven time and again to inhibit limescale formation. Its ability to combat limescale deposits is really quite remarkable, as it both lays down a protective layer on the walls of the supply piping and inhibits future calcium deposits. Because of its ability to provide a protective coating, it’s even suitable for soft water supply pipes - inhibiting corrosion. Siliphos is a food-grade material, and not only is it completely safe to drink, it’s even suitable for babies water. Early Siliphos units (still sold today) are bulky units that have to be topped up every six months and refilled every year. This procedure can result in water leakage. All these negative points were addressed by the introduction of our ‘LimeStop’ range: the LimeStop 600 and the LimeStop 800  LimeStop

In our experience, do they work?



Water softeners

A softener simply removes calcium ions, and replaces them with sodium (salt) ones. Such units are expensive to purchase and install. Artificially-softened water must not be supplied to a potable supply, thus possibly creating an installation headache, as a drinking-water supply has to be provided. Softeners are usually bulky units - taking up a whole kitchen cupboard. They require an electrical supply (usually), a drainage pipe, and constant salt replenishment. They are not considered eco-friendly as they require regular (every few days!) back-flushing with copious amounts of water. Annual servicing is also recommended, meaning on-going expense.

In our experience, do they work?




We cannot make this any simpler: Ask the supplier of your limescale inhibitor if you can return the product after 10 years if your appliance ‘scales-up’. Chances are they’ll just politely tell you that you cannot! So what good is that then? But if in 15, 20 or even 30 years of owning one of our products, your appliance scales-up, then you could have your original purchase cost back. THAT’S a guarantee that it will work.


Both products in our LimeStop range use silicate-polyphosphate - Siliphos:...


The LimeStop 600

Ideal for combination boilers. It is sometimes used by plumbers to protect electric showers and other small water heating appliances. It contains 600g of Siliphos, and comes complete with isolating valves for ease of replacement.


2-year replacement (discounted by £10)


The LimeStop 800

Simply a larger version of the 600, containing 800g of Siliphos – for complete home protection against limescale.


2-year replacement (discounted by £10)


If you’re in any doubt as to which one is right for you, simply email us on and we’ll put you right.




If a manufacturer of a limescale inhibitor or water/aqua conditioner won’t promise to give you your money back in 10 years’ time if you get limescale...





DO NOT BUY a limescale inhibitor unless the makers will give you your money

back - years down the line - if your appliance eventually ‘scales-up’.


Look for this symbol here...




Just 9p a day

keeps limescale away!



“But I’ve heard that ‘this’ water conditioner has undergone trials and has accreditation”


So what? Trials mean nothing - results matter. Secondly, there are ‘standards’ like the German DVGW W512 that have been discredited because trial-testing is carried out under a SINGLE test pattern of one particular flow rate! That isn’t scientific! We’re amused that a particular water treatment company in the UK boast that their product was approved under DVGW W512. Yeah, so what, what’s your point?


Some interesting reads:





Here’s one blurb we particularly enjoyed:

Water is passed in a turbulent state over a very special metal alloy which alters the composition of the water near the alloy surface. This action changes the supersaturating ratio of the water and ensures that lime does not form hard lime scale.”






Watch out for this!

Because with limescale this ‘approval’ means absolutely ZERO!

WRAS is merely the approval of a water fitting, not whether it works or not! Be wary of any limescale inhibitor even displaying it.

Image result for bs detector


You are strongly advised,

when reading the websites

of limescale inhibitor manufacturers, to have your BS detector turned up to maximum.

The saucepan test


We used to advise that you simply look in your kettle to see if you live in a hard water area. However, many modern kettles are very good at keeping limescale at bay, and some people use filtered water in their kettle, so you can’t get a proper indication from the kettle anymore. So this is something we did years ago for a customer - to show up limescale she said she didn’t have. It’s a simple procedure. Just take a small black saucepan, add half a litre of cold water (direct from your cold water tap) and bring to the boil. Boil for 5 minutes, then stand it aside to cool. After it has cooled (about an hour) gently swirl the water in the pan. You should see the calcium move in the bottom. Very gently empty the water to leave just an eggcup-full. You should have a white liquid looking a bit like kaolin, that china-white stuff your mum used to give you to settle your stomach when you were a child.